Conventionally, a liquid electrolyte composition comprising a solvent and an electrolyte salt dissolved therein has been used for electrochemical devices such as a cell, a capacitor, a sensor, a display device, a recording device, etc. However, the electrochemical devices using such a liquid electrolyte composition are unreliable because they often cause leakage or depletion of the liquid electrolyte composition during long-term operation or storage.
Recently, researches have been actively in progress for solidifying the liquid electrolyte composition to prevent the leakage and depletion and to improve the reliability of the electrochemical device. For example, methods where the liquid electrolyte composition is infiltrated into a polymer matrix to prepare a so-called gel electrolyte composition has been disclosed in R. Koksbang et al., Solid State Ionics, 69, 320 (1994), etc. Although this method can solidify the liquid electrolyte composition without reduction of the charge-transporting property of the electrolyte salt, volatilization of the solvent cannot be completely prevented. Further, a so-called, Polymer-in-salt-type solid electrolyte composition, which is prepared by radical-polymerizing a monomer such as a (meth)acrylate monomer in a room temperature molten salt having a low volatility, has been proposed. However, a secondary cell using the Polymer-in-salt-type solid electrolyte composition is insufficient in the cell characteristics, and fisher, preparation of this electrolyte composition requires a polymerization initiator, a radical-generating apparatus such as a light source, etc. to be complicated in operation.